The study focuses on the differences between large and small forms of a rotifer species, Macrotrachela quadricornifera (Rotifera, Bdelloidea), by reviewing the literature and adding further morphological differences. Evidence from life-history traits, growth patterns and trophi (hard structures of the specialized rotifer pharynx) morphology suggests that the large and small forms of M. quadricornifera should not be considered the same species. Macrotrachela vanoyei Schepens, 1954 is re-established as a good species, differing from M. quadricornifera in the smaller size of body, egg and trophi, as well as the number of proximal and distal teeth on the trophi.
